1. Field of the Invention
The present invention relates to a multi-carousel library which has its disk capacity doubled by a unique transport, disk retention device and drive combination.
2. Description of the Related Art
Considerable effort has been made to increase the areal density of storage media, such as magnetic tape and magnetic and optical disks. The read and write heads for magnetic media have been made extremely small by the use of thin film technology. Write heads with a 2-3 .mu.m track width have been proven and submicron track widths appear to be feasible. With the same technology, read heads are fabricated to read narrower than the written track. The track density of a magnetic head is quantified as tracks per inch ("TPI"). Write heads are also made with a very narrow gap, in the order of 0.3 .mu.m, so that the linear density of the head is maximized. This will determine the number of bits per inch ("BPI") written into the magnetic medium as it moves relative to the magnetic head. The product of the tracks per inch density and the linear density is known as the areal density of a head. Areal densities in the order of 1 gigabyte per square inch are now feasible.
While the areal density of recordable media is remarkably high, the libraries which store the media are spatially non-compact. Consequently, in a data storage library the spatial density of stored data can be quite low. A typical data storage library includes a track and trolley combination which carries a cartridge or disk picker for removing or replacing cartridges from place to place within the library. This generally requires two tracks, one along the full length of the library and one along the height of the library. A more sophisticated data storage library includes a robotic arm which may be selectively positioned anywhere within the library for removal or replacement of recordable media cartridges.
A significant improvement in spatial density of stored data was realized by the use of a multi-carousel library. In such a library, the carousels are vertically stacked for independent rotation about a central axis. Each carousel has a plurality of receptacles which are angularly spaced from one another about the central axis for storing the recordable media. A picker operates adjacent the peripheries of the carousels for transporting storage media from the various receptacles to an external drive device. A commonly assigned application on such a library entitled "Sub-Carousel Data Storage Library" was filed on Apr. 16, 1993, Ser. No. 08/048,437, which is incorporated by reference herein. In the previously filed multi-carousel storage library, each receptacle stored only one storage medium. It would be desirable if this capacity could be doubled while still maintaining the multi-carousel concept.